peatt



(No Model.) 2 Sheets-Sheet 1. O. R. PRATT.

ELEVATOR.

Patented Apr. 20. 1897.

Witne ss 25 Inventor, R P H fiharle r'a 221/ ,qfiine 2 Sheets-Sheet 2 C.R. PRATT. ELEVATOR.

Patented Apr. 20, 1897.

(No Model.)

Charis M Inventor,

Witnesses? UNITED STATES ATENT FFICE.

CHARLES R. PRATT, OF NEW YORK, N. Y., ASSIGNOR TO THE SPRAGUE ELECTRICELEVATOR COMPANY, OF SAME PLACE.

ELEVATOR.

SPECIFICATION forming part of Letters Patent No. 580,893, dated April20, 1897.

Application filed November 13, 1891. Serial No. 411,819. (No model.)

To aZZ whom it may concern.-

Be it known that I, CHARLES R. PRATT, a citizen of the United States ofAmerica, residing in the city, county, and State of New York, haveinvented certain new and useful Improvements in Elevators, of which thefollowing is a specification.

My invention is an improvement in elevators, the object of whichismainly to operate cars through distances exceeding the practical limitsof systems now in use, as in high towers, though it is adapted forgenera-1 use.

It consists chiefly in the addition to a suitable traction system ofcertain tension devices. These will be described in connection with atwincar elevator system in which one car is balanced against another andthe two start, stop, and travel together. This is suitable forhigh-tower express elevator service, but for general use one of the carsshould be replaced by a counterweight. Where in the claims I specifycounterbalanced cars I mean two cars which counterbalance each other orone car with a counterweight connected in the manner of another car.

I11 the accompanying sheets of drawings, Figure 1 is a horizontalsection on the line co m of Fig. 2 through an elevator-well containingany system and showing the driving mechanism. Fig. 2 is a verticalsection through the well on the line a x of Fig. 3, showing both cars.Fig. 3 is a vertical section through the well on the line :0 00 of Fig.2, showing one car.

Two elevator-cars 1 and 2 are shown, the one at the bottom and the otherat the top platform, the frame of the well being broken above car 1 andbelow car 2. There are two independent suspension-cables 3 and 4. Eachof the pair of cables is attached to each of the pair ofcars atcorresponding corners or sides and between the cars passes over one ormore sheaves 5 6 at the top of the well. pending-cables thus lie inparallel planes on opposite sides of the car in slotted conduits alongthe sides of the well. Each is a continuous cable, so that there are twobranches between the cars, and in the loops or bights are hung sheaves 7S at the sides of the cars. These sheaves are on the ends of threaded Irods 9 10, which pass through cross-heads 11 The susguideways.

under the cars, which carry nuts 12 at the upper and under sides of thecross-heads. The lower nuts allow an adjustment to coinpensate for.stretch of the cables.

At the lower ends of the threaded rods are sheaves 13 14, over which arethrown the planes of the suspension-cables, though this is notessential.

Starting from the sheave 13 on the lower end of one of the threaded rods9 on car 1, the two sides or branches of one of these tractioncables canbe traced down over tension-sheave 17, thence half-way round drum 18,thence to drum 19, back to 18, again to 19, thence under a secondtension-sheave 20, and finally to the attaching-sheave on thecorresponding threaded rod of car 2. The traction-cables attached to theother sides of the cars pass in like manner over similar sheaves ordrums. By the use of more than one traction'drum the tendency to lateralmovement of the cable along the drums is greatly diminished, and thedrums may be set in different planes, so that the cables shall startaround and leave them in planes at right angles to their axes, thusremoving all tendency to lateral movement of the cables, as is wellunderstood.

All four drums are driven by pinions on the axes of motors 21 22 23. Thepinions on the axis 22 insure positive and uniform speed of the fourdrums, since they gear with all of them.

When the drums are driven by motors, one of the cars is hauled down bythe pair of traction-cables and the other car is hauled up by the pairof suspension-cables In this form of elevator, as above described, twodifficulties are encountered which my invention is designed to obviate.First, if the tension of the cables attached to the two sides of thecars is not the same the cars will be twisted somewhat and will jamagainst the This diiterence of tension may result from many causes, as,for example, a slight inequality in the diameters of the drums. Second,if the heavier of the two cars is ascending the suspending-cables willstretch, and the traction-cables will therefore slacken under this car,and if the heavier car is descending and outweighs the other carsufficiently to drive the whole system the tension-cables will be slackunder it. This slacking throws the cables oft of the tensionsheaves. Inorder to obviate these two difiiculties, a system of tension cylindersand sheaves is introduced. A hydraulic system is shown; but it may bereplaced by a pneumatic system. There are four hydraulic cylinders 26 2728 29, connected with the tanks 30 31 by pipes 32 33. In the tanks arefloats, which control switches and cause the pumps to operate Wheneverthe water falls below a certain limit; or the pumps may operatecontinuously, the overflow being carried into the supply-tank.

To obviate the first diiiiculty, namely, the unequal pull on oppositesides of the same car, the cylinders are connected in pairs by pipes 34,entering above the pistons. Discharge-pipes are shown below the pistons.

. Each pair operates the two tension-sheaves under one of the cars, andif the tension 011 one sheave is greater than the pull on the other thepiston attached to the first sheave will be drawn up and the pistonattached to the second sheave forced down until the tensions areequalized. A straight pull on the car is thus insured.

The second difficulty, namely, slack cable under a car which is heavierthan the counterbalancing car or weight, is also obviated, since as soonas the tension of any cable is less than the pressure exerted by thehead of fluid in the reservoir the piston attached to the correspondingtension sheave will be forced down, and if the pressure is sufficient tomaintain a taut cable and the pipe from tank to cylinder be sufficientlylarge the slack will be taken up almost instantly. For this purpose ahead of about seventeen feet and a pipe about four inches in diameter,onethird the interior diameter of the cylinder, is recommended.

It is not desirable to have a greater pressure than is necessary tomaintain a taut cable. To prevent the piston f rom being drawn up when aconsiderable tension is exerted on the tension-sheaves, a check-valve 35is inserted in each of the pipes between the tank and cylinder andopening toward the latter. This valve is constructed to close wheneverthe pressure within the cylinder exceeds the pressure from the head ofwater. The piston is thus anchored except for such movement as resultsfrom leakage at the piston. Were it not for this check-valve or someequivalent the piston would strike against the cylinder-head.

That I claim, and desire to secure by Letters Patent of the UnitedStates, is-

1. In an elevator, the combination of counterbalanced cars, suspensionand traction cables connecting the cars, and one or more traction-drumsand tension -sheaves connected with the latter cables, andpressurecylinders keeping the cables taut, substantially as described. I

2. In an elevator, the combination of counterbalanced cars, a pair ofcables connecting the cars, and traction and tension mechanism and meansfor equalizing the tension on the two cables, substantially'asdescribed.

3. In an elevator, the combination of counterbalanced cars, a pair ofcables connecting the cars,and traction and tension mechanism, andpressure-cylinders united in pairs and operating the tension mechanism,substantially as described.

4. In an elevator, the combination of counterbalanced cars, pairs ofsuspension and traction cables connecting the cars, and tension andtraction mechanism connected with the latter cables, substantially asdescribed.

5. In an elevator, the combination of counterbalanced cars, pairs ofsuspension and traction cables connecting the cars, and traction andtension mechanism connected with the latter cables, and means forequalizing the tension on the two traction-cables, substantially asdescribed.

6. In an elevator, the combination of counterbalanced cars, pairs ofsuspension and traction cables connecting the cars, and tension andtraction mechanism connected with the latter cables, and pressurecylinders united in pairs and operating the tension mechanism,substantially as described.

7. In an elevator, the combination of counterbalanced cars, pairs ofsuspension and traction cables connecting the cars, and tension andtraction mechanism connected with the latter cables,means for equalizingthe tension on the two traction-cables,and means for anchoring thetension mechanism, substantially as described.

Subscribed by me, this 12th day of November, 1801, in New York city, NewYork.

' CHAS. R. PRATT.

In presence of THOMAS EWING, J r.,

P. F. OSHAUGHNEssY.

